This invention relates to a method of recovering 1-glutamic acid from a solution containing it. In a particular aspect this invention relates to a method of changing the crystal habit of 1-glutamic acid.
1-Glutamic acid in the form of its monosodium salt is an important flavor-enhancing material for foods and is widely used in the preparation of processed foods. One method of preparation is by cultivating an 1-glutamic acid-producing micro-organism, e.g. Brevibacterium divaricatum, on a nutrient fermentation medium, as is known in the art, until the glutamic is produced. When the fermentation is complete, the resulting broth containing the 1-glutamic acid is treated to crystallize the 1-glutamic acid, then centrifuged to separate the broth and the cells of the micro-organism. It is also known to filter the broth to remove the cells prior to crystallization of the 1-glutamic acid.
It is known from J. D. Bernal, Z. Kryst 78, 363 (1931) and S. Hirokawa, Acta. Cryst., 8, 637 (1955) that 1-glutamic acid occurs in two crystal forms, designated .alpha. and .beta.. When a saturated aqueous solution of 1-glutamic acid at 70.degree.C is cooled rapidly, granular or prismatic crystals, the .alpha.-form, are obtained. This crystal form is shown in FIG. 1 and FIG. 2, top view. .alpha.-Crystals are hexagonal in cross-section with a diameter several times the thickness. They would be ideal for industrial processes because of their ease of handling. However their formation on a large scale is difficult and they rearly occur under processing conditions.
On the other hand when a saturated solution of glutamic acid at 90.degree.is cooled gradually so that crystallization occurs at 40.degree.-50.degree.C, needle-like or flaky crystals, the .beta.-form, are obtained. This form is shown in FIGS. 3 and 4. It is the one commonly encountered in industrial processing. The .beta.-crystals are long and flat, i.e. the width and length are much greater than the depth.
These two crystal forms were the subject of an investigation by Yoshiki Sakata reported in a series of papers in Agr. Biol. Chem. 25,829-837 (1961); 26,355-361 (1962); 26,816-823 (1962) and 27,133-142 (1963), which are incorporated herein by reference. Sakata reported that the .alpha.-form was less soluble than the .alpha.-form and as a result, slurries of the .alpha.-form gradually changed into slurries of the .beta.-form.
These plate-like .beta.-crystals pack easily during filtration and hinder additional filtration. Also they do not centrifuge well because they tend to break up, pack and trap impurities in the crystal cake and are difficult to wash. Consequently there is a need for a method of changing the growth habit of glutamic acid crystals to a form which can be more easily filtered or centrifuged.